This invention relates in general to electronic communication buses by which multiple users communicate. It relates more specifically to communication networks in which a two line bus provides a trinary digital, two-way communication path between and among multiple users (nodes) who are in parallel communication with the bus.
The prior art presents many types of bus systems. U.S. Pat. No. 4,337,465 shows a patent primarily for a line driver circuit. It speaks of a three-state cycle, but the three states to which it refers are machine states rather than driver output states. The patent also speaks of random delays to avoid contention, but the random delays are more programmed than hardware controlled.
U.S. Pat. No. 4,282,512 shows a data communication system which employs phase encoded data. It is adaptable to two wire systems. This system monitors transistions at eight times the data transfer rate. "Illegal" transistions are detected by a read only memory. Collisions are detected primarily as being too many transissions or too few transistions.
U.S. Pat. No. 4,281,380 presents a bus collision avoidance system which uses a three part bus: a serial data bus, clock bus and a "busy" status line. The drivers and receivers of this system are differential. The system depends on a priorty scheme which is pre-established among the nodes on the bus.
U.S. Pat. No. 4,271,523 shows another collision detection system, but this system uses coding and decoding techniques to determine collisions. The system employs a carrier which signifies that the bus is busy in between data transmissions.
U.S. Pat. No. 4,262,357 presents a bus system which is controlled by arbiters and selectors.
U.S. Pat. No. 4,199,661 presents a time slot bus system. Each node has a time slot during which time it can seize the bus. Each node has a time slot indicator which is substantially synchronized with every other node.
The bus system, commonly called network, of this invention does not have an arbiter, selector, time slots, priorty scheme, nor a master bus controller. No controller is necessary to supervise and/or schedule nodal access to the bus. While it is true that such a system has the inherent problem of transmission collisions, the system of this invention utilizes a unique means of communicating trinary digital information over the two line bus to detect collisions and to provide un-encoded, self-clocking binary data.
Other attributes and advantages of this invention will be readily apparent upon a reading of the text hereinafter.